1. Field of the Invention
The present invention relates to an automatic focusing camera having a multiple distance measuring function for measuring object distances at a plurality of points in a photographing frame.
2. Description of the Related Art
In general, an automatic focusing (AF) camera detects a distance to an object present at a central portion in the photographing frame, and a photographing lens is moved forward or backward to an in-focus position in accordance with the detected object distance. Therefore, when the object is not present at the central portion of the photographing frame, an out-of-focus state called "central focus error" undesirably occurs. For this reason, another AF camera which comprises a multiple distance measuring function is realized. In this camera, as shown in FIG. 1, distances at a plurality of points in the frame, e g., a central portion (C), a left portion (L), and a right portion (R), are measured to prevent "central focus error" even when the object is not present at the central portion of the frame. A camera of this type selects shortest distance measurement data from the distance measurement data at the plurality of points in accordance with a statistical probability of presence of a principal object to perform focusing.
In a conventional camera, as shown in FIG. 2, a focusing range of a photographing lens is limited at a nearest side (shortest photographing distance do), and an object located at a position nearer than a position corresponding to this distance cannot be focused. Therefore, in the conventional AF camera which selects the shortest distance measurement data, when an object present outside a photographing range (i.e., d&lt;do) enters a distance measurement point, a photographing operation is performed since the camera recognizes that a principal object is present at that point. However, since the object at that position cannot be focused, a photograph which is in an out-of-focus state is consequently obtained. In order to prevent such an out-of-focus photograph, when an object outside a photographing range enters a distance measurement point, a shortest focusing warning is generated to a photographer, or a release operation is canceled, thereby eliminating a photographing error as much as possible.
When the shortest focusing warning is generated when a photographer comes too close to an object, as shown in FIG. 3, he or she can easily understand a meaning of the warning. However, when a photographer is about to photograph a landscape viewed from a window, as shown in FIG. 1, even if the shortest focusing warning is generated since the distance measurement points L and R catch window frames, the photographer may not be able to immediately understand the meaning of the warning and may lose a good shutter opportunity. In this case, if a release operation is forcibly performed, since the camera recognizes the shortest window frame as a principal object, the landscape cannot be focused, and the window frames outside the photographing range cannot also be focused. As a result, an unsuccessful photograph in an out-of-focus state is taken.
In this manner, when the conventional AF camera which selects the shortest distance measurement data catches an object outside the photographing range at a distance measurement point other than a predetermined portion of the frame, a photographer may lose a shutter chance, and tends to take an unsuccessful photograph.